Leaf scorch symptoms on landscape trees infected with Xylella fastidiosa are often confused with similar symptoms caused by stress factors. Because the isolation of X. fastidiosa from trees is difficult and time-consuming, an ELISA test kit for X. fastidiosa was evaluated for reliability and feasibility. The pathogen was detected in all leaf and stem samples collected in June from asymptomatic American elms (Ulmus americana) and American sycamores (Platanus occidentalis) that had had leaf scorch in 26-100% of their canopy during the previous September. The kit was used in a survey of 47 elms. The pathogen was detected in extracts from 17 of 18 diseased trees-12 before and five after symptoms appeared. X. fastidiosa was also detected in extracts from red maples (Acer rubrum), red oaks (Quercus rubra), and red mulberries (Morus rubra) with characteristic leaf scorch symptoms but not in extracts from symptomless trees.